Hydrazonophenol, a Food Vacuole-Targeted and Ferriprotoporphyrin IX-Interacting Chemotype Prevents Drug-Resistant Malaria

Abstract

Rapid emergence of resistance against the frontline antimalarial drugs essentially warrants for the identification of new-generation antimalarials. Here, we describe the synthesis of (E)-2-isopropyl-5-methyl-4-((2-(pyridin-4-yl) hydrazono) methyl) phenol (18) that binds ferriprotoporphyrin-IX (FeIII-PPIX) (Kd = 33 nM) and offers antimalarial activity against chloroquine-resistant and sensitive strains of Plasmodium falciparum in vitro. Structure-function analysis reveals that compound 18 binds FeIII-PPIX through “-C=N-NH-” moiety and 2-pyridyl substitution at hydrazine counterpart plays a critical role in antimalarial efficacy. Live cell confocal imaging using fluorophore-tagged compound confirms its accumulation inside acidic food vacuole (FV) in P. falciparum. Furthermore, this compound concentration-dependently elevates the pH in FV implicating a plausible interference with FeIII-PPIX crystallization (hemozoin formation) by dual-function; through increasing the pH and by binding free FeIII-PPIX. Different “Off-target” bioassays reduce the possibility of promiscuous nature of compound 18. Compound 18 also exhibits potent in vivo antimalarial activity against chloroquine-resistant P. yoelii and P. berghei ANKA (causing cerebral malaria) in mice with negligible toxicity.